Coating the surface of implanted medical devices with polymers and/or therapeutic agents has become a common practice. In 2004, drug eluding coronary stents are expected to comprise more than half of the over four billion dollar worldwide stent market. Therapeutic agents can enhance the intended effect of the medical device, reduce or eliminate infection or inflammation related to the device, accelerate or improve acceptance of the device by the body, and/or treat specific diseases at the site of the device.
Medical devices which are implanted into the human body and whose function can be enhanced by therapeutic coatings include artificial joints, fixation devices such as bone implants, artificial heart valves, pacemaker leads, dental implants and stents including cardiovascular, esophageal, and biliary.
Polymers and coatings such as phosphorycholine, hydrogels and hydroxyapatite, with and without additional therapeutic agents, are commonly placed onto the surface of medical devices at the point of manufacture. While this practice delivers the device ready to use at the point of care, the coating and/or therapeutic agents are subjected to the device sterilization process and the rigors of handling, shipping and storage. Many therapeutic agents, such as proteins, cannot survive the device sterilization. Also, many therapeutic agents have relatively short shelf lives compared to the device itself, and when placed on the device at the point of manufacture, limit the shelf life and storage condition of the device.
Larson et al., in U.S. Pat. No. 6,309,380, address the device point of manufacture therapeutic coating limitation problem by providing for application of the therapeutic coating at the point of care where and when the device is placed into the patient's body. This is accomplished by coating the device at the point of care immediately prior to implantation with a polymer and/or therapeutic agent and converting the coating to a film by a chemical process or energy source such as heat or UV light. Larson et al. do not provide for applying a coating and/or drug to the device at the point of care in a manner that reproducibly controls the device sterility and factors affecting variability of the coating, and subsequently the drug delivery after implantation of the device.